Fire detecting cable



Patented Nov. 29, 1949 UNITED 2,489,293 FIRE DETECTING CABLE Willis G.Holmes,

Filtesearch corporation of 9 Claims. 1

This invention relates to improvements in fire detectors orheat-sensitive mechanisms of the wire or line type, the sensitivity ofwhich extends along their entire length. The advantages of detectors ofthis type in comparison with detectors of the unit or spot type havelong been recognized; and these advantages have been shown to be ofparticular importance in connection with the detection and warning offires on aircraft in fiight. Such line or continuous type detectors haveheretofore generally been capable of one operation only. Once operatedthey remain so until replaced; hence they are incapable of showing whenthem to operate has ceased to exist. On aircraft in flight thisself-restoring feature is of particular advantage. If fire occurs inflight and can not be promptly extinguished, an emergency or crashlanding is necessary. If on the other hand the fire can be extinguishedwith reasonable promptness, the aircraft may proceed to a normal landingat the first available field. To know that a fire has been extinguishedtherefore becomes of very great importance.

Many modern aircraft are equipped with fire extinguishing systems havingsufficient extinguishing agents for more than one attack on fire beforelanding. even if a fire flashes back or breaks out anew after oneattempt at extinguishment, there is avoid a crash landing if theremaining extinquishing agent can be applied at the right time. Againthe advantages of a self-restoring detector are apparent.

Aircraft fire detectors now in use are of both the unit and the line orcontinuous type, the former being generally self-restoring and thelatter being generally of the single operation type. Due to the extremedraft conditions on aircraft in flight, unit detectors to be effectivehave to be placed so close together that they present difficult problemson that account. The line or continuous type detectors used have notonly had the disadvantage of not being self-restoring but have also beensubject to false alarms.

Objects of the present invention are to overcome the aforesaiddifficulties and to produce a detector of the line or continuous typewhich is simple and economical in construction, which is self-restoringand capable of repeated operation, which is durable and reliable in use,which is highly resistant to vibration such as encountered on aircraft,which is unaffected by gasoline. oils and other agents commonly presenton airstill a chance to allay it and Pembroke, Mass" Corporation,

Massachusetts Application July 16, 1946,

assignor to Pembroke, Mass a Serial No. 684,058

craft, which is positive in action and reliable in use, which isresponsive to a fire anywhere along its length, which opens and closesquickly and positively, which can be directly incorporated inconventional electrical circuits to actuate signal lights or other alarmsignals without special instruments, which can be readily installed andserviced and which is generally superior to fire detectors of thecharacter above referred to.

The present invention involves a fire detecting cable comprising innerand outer conductors with a space therebetween and a series ofthermostats distributed along the cable in the aforesaid space,

thoroughly each thermostat having terminals electrically connected tothe conductors respectively and thermostatic means for electricallyinterconnecting the terminals, whereby the circuit comprising theconductors is closed by application of heat to the cable and remainsclosed only so long as heat is applied. Preferably the thermostats areof the snap type and comprise unitary devices with aligned openings sothat they along the inner conductor. In the preferred embodiment eachthermostat comprises a conducting sleeve slidingly fitted around theinner conductor, two conducting rings surrounding the sleeve andelectrically connected to the two conductors respectively, andinsulating means between the sleeve and the ring connected to the outerconductor, one of the conducting rings snapping into contact with theother in response to change of temperature, and the sleeve having headson its opposite ends to hold the in position, one of the headspreferably being in the form of a nut threaded on the sleeve.

For the purpose of illustration a typical embodiment of the invention isshown. in the accompanying drawing in which Fig. 1 is a longitudinalcentral section through one end of a cable;

Fig. 2 is a section on line 2-4 of Fig. 1; and

Fig. 3 is a diagram illustrating the circuit connections.

The particular embodiment of the invention chosen for the purpose ofillustration comprises inner and outer conductors i and 2 and a seriesof thermostats each of which comprises a con-,

two insulating rings 9 and I and a conducting ring ll between the nut Iand the ring ll. To in- -sure good conducting relationship between theconductor 2 and the ring 8 one or more conducting spring pieces I! maybe set in recesses in the periphery of the ring 8. Whether or not thesprings I2 are provided, the outer conductor 2 is preferably drawntightly around the rings 5. Good electrical contact may be establishedbetween the inner conductor i and the sleeve 3 in various ways, as byproviding the respective parts with a contact surface such as silver orpalladium, welding the respective parts together after assembly.assembling while the sleeve is expanded with heat, or using for theinner conductor spring wire having a marked inherent curvature.

While any suitable construction may be provided at the end of the cable,the construction is outer conductor at It periphery of the ring I snapsinto engagement with the'end of ring 6 in response to change oftemperature. While the thermostatic diSks 1 may be constructed to closecircuit tact with the ring 6 in response to heat. diagram oi Fig. 3 thethermostatic disks 1 are indicated diagrammatically at 1, the largerconducting rings at 6, the inner and outer conductors at l and 2, thesource of current at I8 and a signal device at I9. As will be evidentfrom Fig. 3 the signal circuit may be closed in response to any one ofthe thermostats along the length of the cable in response to heat andthen opened again when the temperature falls again.

It will be understood that In addition to the aforesaid advantages, thishammering without damage and no endwise pressure is necessary becausethe thermostatic elements do not need to be held in contact with eachother. ing the ends of the outer conductor internal corrosion mayreadily be prevented.

It should be understood that the present disclosure is !or the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

I claim: 1. A fire detecting cable comprising inner and outer conductorswith a space therebetween, and a series of switches distributed alongthe cable in outer coaxial ductors respectively, being made orthermostatic material ductors respectively, tween said sleeve andaceaaca inner conductor, each switch comprising a conducting sleeveslidably fitting around said inner conductor, two conducting ringssurrounding the sleeve and electrically connected to the two conductorsrespectively, and insulating means between said sleeve and the ringconnected to the outer conductor, one of the conducting rings being madeof thermostatic material and snapping into contact with the other inresponse to change of temperature, said sleeve having heads on itsopposite ends to hold said rings and insulating means in position.

7. A fire detecting device comprising a conducting sleeve having anaxial opening extending therethrough, a conductor in said opening, twoconducting rings surrounding the sleeve, one of the rings being largerthan the other, and insulating means between said sleeve and the largerring, the smaller ring being made of thermostatic material and snappinginto contact with the larger ring in response to change of temperature.

8. A fire detecting device comprising a conducting sleeve having anaxial opening extending therethrough, a conductor in said opening, twoconducting rings the rings being larger than the other, and insulatingmeans between said sleeve and the larger ring, the smaller ring beingmade of thermostatic material and snapping into contact with the largerring in response to change of temperature, said sleeve having heads onits opposite ends to hold said rings and insulating means in position.

9. A fire detecting cable comprising inner and outer coaxial conductorswith a space therebesurrounding the sleeve, one of 25 tween and a seriesof switches distributed along the cable in said space, each switchcomprising two conducting rings surrounding the inner conductor andelectrically connected to the two conductors respectively, one of theconducting rings being made of thermostatic material and moving intocontact with the other in response to heat, whereby the circuitcomprising said conductors is closed by application of heat to the cableand remains closed only so long as heat is applied.

WILLIS G. HOLMES.

REFERENCES c'rrEn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

